Burying rusty nails adds iron that greens up plants and turns hydrangeas blue.
Contested
Rusty nails won't green up your plants or turn hydrangeas blue. Yellow leaves usually mean iron is locked up by high pH, not missing — and a nail's iron isn't available anyway; hydrangea blue is an aluminium-and-pH effect, nothing to do with iron. Soil-test first, then lower pH (elemental sulfur) or use a chelated-iron feed for yellowing, and acidify the soil to blue a hydrangea.
What is actually known
Two separate claims ride on this, and both miss. Yellowing leaves (chlorosis) are usually not a shortage of iron in the soil — most soils hold plenty — but iron that is *locked up* and unavailable because the pH is too high; a rusty nail adds a trace of slowly-oxidising metallic iron that is itself not plant-available, so it does nothing for the yellowing. And hydrangea colour is not an iron effect at all: blue flowers come from *aluminium* the plant takes up in acidic soil, pink from aluminium being unavailable in alkaline soil — iron is not the lever. The real fixes are set by a soil test: to free up iron, lower the pH (elemental sulfur) or use a chelated-iron foliar feed; to blue a hydrangea, acidify the soil (often with aluminium sulfate), which is about pH and aluminium, not nails.
Evidence: not yet confirmed against its 4 sources.
what this rests on - 4 pointers
iron chlorosis is usually pH-induced unavailability
not a soil iron shortage
and metallic iron from nails is not plant-available; hydrangea sepal colour is controlled by aluminium uptake under acidic pH
not iron; extension consensus
When would that grow at your place? →
Cite this page
Milpa Gardens. "Burying rusty nails adds iron that greens up plants and turns hydrangeas blue." Evidence grade: Contested. https://milpa.garden/beliefs/rusty-nails-iron-plants/
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